The invention relates generally to an improved ion source comprising a magnetron in conjunction with a Penning cell, for producing highly collimated ion beams. The ion beams result from ionizing gases such as helium, argon, nitrogen, carbon oxide(s) and fluorides and sputtering a wide variety of target materials, including metals, alloys, borides, and nitrides. The invention also relates to producing ion beams rich in boron ions by sputtering a boron-containing target in an ion source in which the target has thick dimensions that provide the ion source with an extended life. The resulting boron ion beam can be useful for applications such as thin film deposition and ion implantation.
There is a continuing need to provide ion sources which produce ion beams that are highly directional and/or collimated. The ion beams can be used in a variety of applications such as in the manufacture of semiconductors, thin film deposition and surface modification via ion implantation.
Boron is an important constituent in thin film depositions on optical and electronic recording surfaces and as a dopant in the manufacture of semiconductor circuits and components. Boron is usually processed as boron ions formed by dissociating a boron target in the plasma of an ion source. Typically the ions are extracted from the ion source employing boron trifluoride as a source of ions. The boron ions are usually separated in a mass analyzer, and transported through an ion accelerator, employing apparatus well-known to the industry.
Boron trifluoride, however, is a hazardous material classified as a poison and as a non-flammable gas. It is toxic when inhaled and severely corrosive to the skin, eyes and mucous membranes, causing serious burns on contact. In certain instances, a ceiling limit of 1 ppm (parts per million) gaseous boron trifluoride may be imposed for handling this gas in air. In addition, the handling of boron trifluoride requires training and special safety precautions, special clothing and safety apparatus. Personnel are required to change or replace components of the ion source or gas cylinders and their supply lines to the equipment, causing them to handle parts previously exposed to poisonous boron trifluoride gas.
In addition, dissociated fragments of boron trifluoride can be severely corrosive to the ion source, beam line components, and associated equipment such as vacuum pumps and vacuum valves can be severely affected by the corrosion, thus reducing the operational time. Users of equipment employing boron trifluoride as a source of boron might expect to replace or rebuild the filament after 24 beam hours in high flux boron ion sources. A long tool life between maintenance and high stability are vital characteristics for the operation of such ion sources on a production line.
The potential toxic and corrosive aspects arising from using boron trifluoride are major obstacles to improving the life span of a traditional boron ion sources and its associated equipment. Thus, there is a need for an ion source capable of producing boron ion beams while maintaining an improved tool life for extended periods of time.
One aspect of the present invention provides an ion source. In one embodiment, the ion source comprises a magnetron disposed in a first housing being constructed and arranged to produce a radial magnetic field coaxial with an axial electric field. A positively charged, sputtered ion beam is provided from the magnetron. A cold cathode sputtering target is disposed in a second housing in which the second housing is constructed and arranged to produce a radial electric field and an axial magnetic field for collimating the ion beam from the magnetron. The radial electric field and axial magnetic field are coaxial with each other and with a direction of the sputtered ion beam which is normal to a planar surface of the cold cathode.
Another embodiment of the ion source of the invention comprises a magnetron for generating a magnetic field and a cathode having a planar face positioned adjacent the magnet ion. The cathode comprises a cold cathode sputtering target and comprises a material by which a positive ion beam is formed. The ion source further comprises a collimator comprising trapped electrons for collimating the ion beam, the trapped electrons and the ion beam being coaxial with each other.
Another embodiment of the ion source of the invention comprises a magnetron having an axis, constructed and arranged to produce a magnetic field radial with respect to the magnetron axis, and coaxial with an axial electrical field with respect to the magnetron axis, for providing a positively charged, sputtered ion beam from the magnetron. The ion source further comprises a Penning cell including a cold cathode sputtering target and having an axis, the Penning cell being constructed and arranged to produce an electric field radial with respect to the Penning cell axis and a magnetic field axial with respect to the Penning cell axis and being positioned to collimate the ion beam from the magnetron. The Penning cell has a radial electric field and axial magnetic field coaxial with each other. A direction of the sputtered ion beam is normal to a planar surface of the cold cathode.
Another embodiment of the ion source of the invention comprises a magnetron for generating a magnetic field and a cathode comprising a cold cathode sputtering target and comprising a material by which a positive ion beam can be formed. The cathode is positioned relative to the magnetron so as to be able to form a positive ion beam involving crossed magnetic and electric fields generated by the magnetron. The ion source further comprises a collimator able to trap electrons for collimating the ion beam, the collimator being positionable such that the trapped electrons and the ion beam are coaxial with each other.
Another aspect of the present invention provides a cold cathode comprising a boron-containing, sputtering target material with a bore through on axis, for use in an ion source. The material is selected from the group consisting of a boron alloy, a boride, and mixtures thereof.
Another embodiment of the ion source of the invention comprises a single solid disc electrode. The solid disc electrode comprises a boron-containing material selected from the group consisting of a boron alloy, a boride, and mixtures thereof.
Another embodiment of the ion source of the invention comprises an array of at least two disc electrodes. Each electrode comprises a boron-containing material selected from the group consisting of a boron alloy, a boride, and mixtures thereof.